In order to illustrate the circumstances of this attack, I have produced an
AGI Viewer file (see bottom of this page for more
information on AGI Viewer) which confirms the basic facts reported by
AW&ST. It shows the period from 2007 January 11 at 22:26:10 UTC (which
analysis shows as the most likely time of the event, slightly different than the
time of 22:28 UTC reported by AW&ST) until January 12 at 0600 UTC. The
orbit of FENGYUN 1C (pre-attack) is shown in red and the location of the Xichang
Space Center is also shown. I am also providing a Google
Earth location file for the Xichang Space Center, with recently released
details of the launch complex and surrounding facilities.

FENGYUN 1C and the other pieces of debris now
catalogued by NORAD are shown in
green. From this animation, it is easy to see the spread of the resulting debris
cloud for the first couple of orbits. It should be noted that the spread of
debris at the time of the event is due to the error associated with propagating
the TLEs back from the time they were released to the time of the event.

As of 2012 June 22 (another 10 TLEs were released on this date), 3,312 pieces
of debris—including whatever's left of the original payload—have
been catalogued by NORAD. Only 256 have decayed as of this date. That makes this
event the largest debris-generating event on record—far surpassing the 713
pieces cataloged when the Pegasus rocket body that launched STEP 2 exploded on
1996 June 3. NASA's Orbital Debris Program Office now estimates more than
150,000 pieces of debris larger than 1 cm from this event:

Updating the initial analysis by CSSI just after this event was first
reported shows pieces in the debris cloud ranging from below 200 km in altitude
up to almost 4,000 km (see Gabbard plot), posing
a threat to many operational satellites, due to the polar orbit of the debris
cloud. Potential conjunctions with satellite payloads currently on orbit can be
found by searching for "FENGYUN 1C" using SOCRATES
or by generating an
automatic search.
Using the SOCRATES run from 2008 January 22 at 1300 UTC, there were 3,100 occasions
predicted where a piece of FENGYUN 1C debris would come within 5 km of a
satellite payload in low-Earth orbit over the next week—over 28 percent of
all predicted conjunctions over that period. We are now routinely seeing about
3,000 conjunctions within 5 km over a seven-day period between the FENGYUN 1C
debris and payloads in Earth orbit.

The figures below (from 2007 December 5) give a sense of the risk to other
satellites in low-Earth orbit (LEO), including the International Space Station
(ISS). The first figure shows how the orbit of the ISS passes through the ring
of debris at the southern part of its orbit. The second figure shows the larger
population of LEO satellites—payloads, rocket bodies, and debris (size
exaggerated for visibility)—which could also be affected.

This debris event is so large that the debris can still be fairly easily seen
without doing anything to emphasize the debris cloud, although the debris ring
has widened considerably over the past eleven months.

View of All Satellites including Debris Ring from Chinese ASAT Test Readily Visible

As of 2008 January 22, an analysis of the current SATCAT shows there are 3,231
payloads in Earth orbit or beyond (see SATCAT
Boxscore for details). Of those, we have orbital data for 2,864 payloads in
Earth orbit. Of the missing 367 objects, some are in deep-space orbits around
the Sun or other planets and some are not released by the US government, for
whatever reasons. Of the 2,864 payloads we do have data for, 1,899 of these
payloads pass through the regime now affected by the debris from the Chinese
ASAT test—fully two-thirds of all payloads in Earth orbit.

Despite several statements by NASA officials that the ISS is not at risk due
to this event, UPI reported 2007 February 2 that US and Russian officials
maneuvered the ISS specifically to avoid a piece of debris from this event. For
details on this report, see:

At this point, however, I am unable to independently verify this story via
official sources at NASA or the Russian Space Agency and
analysis of the TLE data for 2007 does not
support the claim that the ISS has been maneuvered since the ASAT test was
conducted. UPI subsequently revised their original story to say that the Russian
Mission Control Center spokesman "was describing a general policy." (The ISS was
maneuvered on 2007 March 15 in preparation for the arrival of Soyuz-TMA 10, as
reported in
ISS
Status Report SS07-13.)

The first acknowledged maneuver to avoid a piece of debris from the Chinese
ASAT test occurred on 2007 June 22 when flight controllers at NASA's Goddard
Space Flight Center briefly fired the thrusters on their TERRA satellite to
avoid a 7 percent chance of being struck the following day:

Several analysts have suggested that the debris from this event would be
relatively short-lived and only remain in orbit for ten years or less.
Unfortunately, nothing could be further from the truth. A detailed analysis of
the orbital lifetime, performed on 2007 October 10, of the debris cataloged so
far—using the Lifetime model implemented in STK—predicts that just
over 6 percent of the debris (136 pieces) will have decayed within ten years and
79 percent will still remain in orbit 100 years from now. As of 2008 January 22,
only 23 of the 2,377 pieces cataloged to date are shown as having decayed from
orbit—less than one percent in the first year. The majority of the debris
from this one event will remain a hazard for centuries to come. (Note: This
analysis was only done for 2,150 of the 2,247 pieces catalogued as of 2007
October 10 since it appears that 97 pieces were missing from the catalog at that
time.)

The graph below shows a prediction of the percent of the total Chinese ASAT
test debris population which has decayed from orbit over time based on our
analysis. The baseline orbital lifetime analysis results are shown in blue along
with high-drag (upper line) and low-drag (lower line) excursions to help assess
the impact of uncertainty in the baseline assumptions.

Plot of Orbital Decay Rate of ASAT Debris

Without specific information on size, mass, and shape of individual debris
pieces resulting from this test, it was necessary to make a number of
assumptions to complete the orbital lifetime analysis. First, it was assumed
that all pieces were large enough to be tracked by US SSN (approximately 10 cm)
which, given the size of the original satellite, meant that each piece would be
roughly the same size. Assuming they had roughly the same densities, the total
dry mass of the satellite prior to the test (850 kg) was divided by the number
of pieces in the public SATCAT (2,247) at that time, yielding an average mass of
0.38 kg. These assumptions were used for the baseline analysis.

Next, it was necessary to select an appropriate atmospheric model to estimate
drag. STK has nine atmospheric models which can be used in its Lifetime tool.
Sensitivity analysis using the various models showed differences on the order of
months, which was expected (and can be seen from the graph) to be a small
difference when compared to the overall lifetime of most of the pieces.
Therefore, the Jacchia-Roberts model was chosen, since it is an analytical model
and runs much faster than the other models, most of which are numerical or not
as sophisticated.

The analysis used the latest Schatten space weather predictions for the
period 2006 October until 2030 May. STK/Lifetime replicates this cycle
throughout the analysis period beyond the Schatten predictions
(2030–2107). In fact, the effects of the solar cycle can be seen
throughout the curves in the graph above, especially in the high-drag case.
Considerable variability is likely in these predictions, though, since our
ability to predict solar and geomagnetic cycles is still quite crude. The
impact, however, should not be as significant for the majority of debris pieces,
which are above the original FY 1C orbit. In fact, the chart supports this
assumption since the variability due to the solar cycle is far less than the
uncertainty in the drag due to the ballistic coefficients of the debris.

The baseline analysis also assumed a coefficient of drag of 2.2. However, due
to the uncertainty in the size, mass, shape, and coefficient of drag for each of
the pieces, additional runs (excursions) were conducted which varied the
ballistic coefficient by a factor of two relative to the baseline assumptions.
That is, the ballistic coefficient—which is the product of the coefficient
of drag and the cross-sectional area divided by the mass—varied from half
the baseline ballistic coefficient (low-drag case) to twice the baseline value
(high-drag case). The results indicate that while there may be considerable
variability due to the uncertainty in the debris characteristics, even doubling
the drag on all the debris still only results in 36 percent of the debris
decaying from orbit within 100 years.

As of 2009 June 10, only 50 pieces of this debris have decayed from Earth
orbit.

An excellent one-minute video (42,414,214 bytes bytes, HD WMV format, playing
time 1:31) of the Chinese ASAT test and resulting debris (1,710 pieces shown) is
also available, courtesy of AGI's video team. This video is a 2007 Film/Video
Silver Winner of the 28th Annual Telly Awards!

Larger versions of all the images provided on this page are available by
clicking the images. The interactive AGI Viewer files of these scenes are also
provided to give you a far better sense of the overall environment by allowing
you to zoom in and out and move around the Earth while watching all the
satellites moving in their orbits.

Note: AGI Viewer is a free product which allows anyone
with a Windows computer to view an STK (Satellite Tool Kit) scenario. With it,
you can animate a scenario forward or backward, pause the animation, and zoom or
pan the view for a more complete understanding of the event. Just like with
Adobe Acrobat, where the authoring software requires a license but the Adobe
Reader is free, STK can produce AGI Viewer files—also known as
VDFs—which can then be viewed by anyone with the AGI Viewer software. You
can find the free AGI Viewer on the AGI web site at
https://www.agi.com/stk-viewer. - TS